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A differential scanning calorimeter was used to determine freezing temperature of rough rice. Rice grains with a moisture content of 22.1% froze at about 35C. Rice grains with a moisture content of less than 20.8% did not freeze at a temperature of 55C. Incidence of freezing injury of rice grains was determined by germination rate because grains that suffered from freezing injury did not germinate. Rice grains with a moisture content of less than 17.8% germinated after being stored at 80C for 11 days. Thus, no grain with a moisture content of less than 17.8% froze at a temperature of 80C.

Effects of temperatures between 50C and 25C on physiological properties and quality characteristics of rough rice during four-year storage were investigated. Low temperature maintained vitality of rice, minimized physiological activities, starch deterioration and rancidity in rice, and consequently preserved rice quality. Eating quality of rice stored at temperatures less than 5C for four years was the same as that of newly harvested rice. These results indicate that preservation of rough rice quality for several years is possible by storing rice at an average temperature below 5C during storage. A new on-farm rice storage technique at temperatures below ice point by using natural fresh chilly air in winter has been in practical use in Hokkaido, the northernmost island of Japan, in recent years. Twenty-six grain elevators have been constructed in Hokkaido since 1996. The storage capacity of rough rice in 2004 was 115,000 t.